Pontiac 1999 Firebird - Manual (Page 254)

yellow blue
6-6
Filling Your Tank
The cap is behind a hinged door on the driver’s side of
your vehicle.
CAUTION:
Gasoline vapor is highly flammable. It burns
violently, and that can cause very bad injuries.
Don’t smoke if you’re near gasoline or refueling
your vehicle. Keep sparks, flames and smoking
materials away from gasoline.
To remove the cap, turn it slowly to the left
(counterclockwise). The cap has a spring in it; if you let
go of the cap too soon, it will spring back to the right.